Inverter devices are used to drive the driving motors of electric automobiles and other electric vehicles. These inverter devices include an electrical circuit in which switching elements are connected using a bridge-circuit configuration. Inverter devices turn the switching elements of the bridge circuit on and off as appropriate and execute the switching of current made to flow to the driving motor. Power transistors, IGBT, FET, and the like are widely used as the switching elements that constitute the bridge circuit. These inverter devices are usually configured in a modular structure in which a plurality of switching elements is housed in one package.
The operation of the driving motor of an electric vehicle is characterized in that a large current flows to the switching elements that constitute the bridge circuit, and a surge voltage is generated from the on/off operation. The length of the wiring that constitutes the electric current pathway is therefore made as short as possible when the plurality of switching elements is mounted inside one package in the inverter device, whereby resistance in the wiring is minimized, and the value of the inductance that is an electrical characteristic of alternating current is reduced.
A well-known example of a conventional semiconductor device having a modular structure similar to the aforedescribed inverter device is the semiconductor device described in Japanese Patent Application Laid-Open Publication No. 2002-26251. The semiconductor device described in Japanese Patent Application Laid-Open Publication No. 2002-26251 has three electric terminals: a high-voltage external electric terminal, a low-voltage external electric terminal, and an output external electric terminal. These three electric terminals all have a rectangular plate shape as the planar shape and are positioned in an overlaid state with gaps in between so as to be positioned in parallel. The output external electric terminal is positioned between the high-voltage external electric terminal and the low-voltage external electric terminal. The structure is such that semiconductor chips (switching elements or the like) are sandwiched between two adjacent electrical terminals from among the three electrical terminals. The high-voltage external electric terminal and the low-voltage external electric terminal are formed to extend towards the same end, and the output external electric terminal between these terminals is formed to extend towards the other end on the opposite side.
The connection between the semiconductor chips and the electrical terminals in the semiconductor device described in Japanese Laid-open Patent Publication No. 2002-26251 bridges a short distance, and therefore voltage drops resulting from internal wiring are reduced. This semiconductor device is also characterized in that the direction of current flowing to the high-voltage external electric terminal and the direction of current flowing to the low-voltage external electric terminal are opposite, and therefore the orientations of the magnetic fields generated by those currents are opposite, and inductance can be reduced.
The inverter device of a three-phase motor is provided with a high-side (high-voltage) semiconductor chip and a low-side (low-voltage) semiconductor chip for each of the U, V, and W phases and contains a total of six semiconductor chips. This inverter device is provided with a semiconductor module in which two semiconductor chips, high-side and low-side, are packaged for each phase. The high-side semiconductor chip and the low-side semiconductor chip of this semiconductor module will not short circuit during use in controlling a motor, and therefore current will not flow to the high-voltage electrical terminal and the low-voltage electrical terminal at the same time. In other words, the bridge circuit either contains an electric current pathway from the high-voltage electrical terminal through a semiconductor chip to the output electrical terminal, or an electric current pathway from the output electrical terminal through a semiconductor chip to the low-voltage electrical terminal. A problem is therefore presented in that reducing inductance is difficult when the configuration of the semiconductor device described in Japanese Patent Application Laid-Open Publication No. 2002-26251 is applied to controlling a motor using the inverter device of a three-phase motor.
The control substrate (the substrate on which the gate driver is mounted) for controlling the semiconductor chips must be positioned externally with respect to the module in the modular structures of the prior art. The length of control wiring to the control substrate from a control electrode leading from a gate electrode has therefore tended to increase. Problems have therefore been presented in that the wiring inductance increases, and anti-noise performance deteriorates. The control substrate, which is a separate unit from the module, also requires fastening members, a case, and the like, and problems have been presented in that the overall size of the semiconductor device increases.
The ability to reduce the inductance of the main circuit, improve the anti-noise properties of the driving signal, and make the modular structure smaller and more compact in the structure of a semiconductor module in which a plurality of semiconductor chips is mounted in one package has therefore been needed in the aforedescribed semiconductor device.